Drop former for intravenous set

ABSTRACT

A drop former for use with the drip chamber for an intravenous set for determining the flow rate of a parenteral fluid. The drop former has a parenteral fluid passage formed therethrough having an inlet opening for communicating with a source of parenteral fluid and an outlet opening for communicating with the drip chamber. The parenteral fluid passage defines a drop forming orifice for forming drops of parenteral fluid of predetermined size having an outlet opening at least as large as its inlet opening. The drop former is formed form a plastic which absorbs less than about 0.03 percent by weight water.

[451- Mar. 4, 1975 United States Patent [191 Noiles et a1.

Hendricks............. Scislowicz.....

141/330 128/214 C Schne11er.........,.... 141/114 X nm we "a Mu JB 67 67 999 111 57 l. 885 704 862 8 9 LJ 333 DROP FORMER FOR INTRAVENOUS SET[75] Inventors: Douglas G. Noiles, New Canaan;

Anthony D. Spasiano, Greenwich, both of Conn.

[73] Assignee: United States Surgical Corporation,

Baltimore, Md.

July 3, 1973 Primary Examiner-Henry T. Klinksiek Attorney, Agent, orFirm-Fleit & Jacobson [22] Filed:

[57] ABSTRACT A drop former for use with the drip chamber for an 211Appl. No.: 376,227

intravenous set for determining the flow rate of a parenteral fluid. Thedrop former has a parenteral fluid passage formed therethrough having aninlet opening for communicating with a source of parenteral fluid and anoutlet opening for communicating with the drip chamber. The parenteralfluid passage defines a Mu mm; ISM H ,1 Qm 75 1 37. 26C3 l ,2 33 5 R3 5m i 7 UM 3 "i3 1M9 5 MSW. mm mmU4 WW H mw 4 H c n w H n S L M l H S Ul Fdrop forming orifice for forming drops of parenteral [56] ReferencesCited UNITED STATES PATENTS fluid of predetermined size having an outletopening at least as large as its inlet opening. The drop former isformed form a plastic which absorbs less than about 0.03 percent byweight water.

.771,9l3 Flasnocker... 141/331 X Beddow 141/337 22 Claims, 7 DrawingFigures PATENTED 75 SHEET 2 or 2 Fig.2

Fig.3

'i lrlfd 6 Q 2 Q 1 DROP FORMER FOR INTRAVENOUS SET BACKGROUND OF THEINVENTION The present invention relates to an improved drop former foruse with a drip chamber of an intravenous set.

Intravenous sets for the introduction of parenteral fluid throughvenipuncture typically include a piercer for insertion into a parenteralfluid container, a flexible plastic tube for transporting the parenteralfluid from the container to the patient, and a needle adapter to whichan intravenous needle is attached. The typical intravenous set alsoincludes a clamp which closes the internal bore of the flexible tubingto control the flow rate of the parenteral fluid. The flow rate isdetermined by a flow meter, such as a drip chamber, positionedintermediate the piercer and the needle adapter and upstream of theclamp.

The piercer is conventionally formed from a relatively rigid plasticsuch as styrene-acrylonitrile, nylon or rigid polyvinyl chloride, andincludes a piercing member having a sharp end for piercing the closureof a parenteral fluid container. A parenteral fluid passage is providedin the piercer for transferring parenteral fluid from the container tothe intravenousset, typically directly into a drip chamber. The piercermay also be provided with a vent passage for venting the container whenthe parenteral fluid container does not have a separate vent tube. Whena drip chamber is used as the flow meter, the discharge opening of theparenteral fluid passage in the piercer comprises a drop forming orificefor forming drops of predetermined size. The drops emerge from the dropforming orifice and fall through the drip chamber, where they arecounted and the flow rate of the parenteral fluid determined.

Smaller size drops are preferred in certain applications, particularlyfor intravenous sets used in pediatric applications, and so the dropforming orifice of the piercer is frequently adapted to accept a plasticplug containing a very small diameter metal tube or cannula which willform a smaller size drop. This cannula typically forms 60 drops permilliliter whereas the drop forming orifice of the piercer will normallyform l2, 15 or 20 drops per milliliter. Accordingly, the use of thecannula enables a much more accurate measurement of small flow rates. Inother cases a plastic insert having a tapered parenteral fluid passagehas been used in place of the plug and cannula. The plastic insert hasan inlet opening of somewhat similar size to the discharge opening ofthe piercer and a smaller outlet opening of similar size to the bore ofthe cannula. In these cases, the insert has been formed from a plasticsuch as polyethylene.

It has been found that the size of the drops formed at the parenteralfluid discharge opening of a conventional piercer varies significantlywith time. More specifically, variations of 5 to percent have beenobserved over a twenty-four-hour period, In general, it has been foundthat the drop size becomes larger with time. Further, it has beenobserved that the size of the drops formed with the plastic insert forpediatric use not only varies with time, but with flow rate and that asthe flow rate becomes higher, the drop size becomes smaller. Nosignificant change in drop size has been observed with respect to themetal cannula; however, it is not feasible to use a metal piercerbecause of cost considerations and because the intravenous set isdiscarded after one use. Also, it is not feasible to form a drop formerfor insertion into the parenteral fluid discharge opening of a piercerfrom metal because of the difficulty in properly shaping a small metalinsert and the difficulty in attaching the metal insert to the plasticpiercer.

In view of the foregoing, an object of the present invention is toprovide an improved drop former for use with the drip chamber of anintravenous set.

A further object of the present invention is to provide a drop formerfor an intravenous set which forms drops of predetermined size, whichsize does not vary significantly with time or flow rate.

Still another object of the present invention is to provide a dropformer for an intravenous set which can be inserted into the parenteralfluid discharge opening of a conventional piercer.

Yet another object of the present invention is to provide a drop formerwhich is adapted to receive a conventional metal cannula for formingdrops of suitable size for pediatric use.

Still another object of the present invention is to provide aneconomical drop former which can be easily fabricated and will carry outthe other objects of the present invention.

SUMMARY OF THE INVENTION The present invention relates to an improveddrop former having a parenteral fluid passage with an inlet opening forcommunicating with a source of parenteral fluid and an outlet openingfor communicating with a drip chamber. The parenteral fluid passagedefines a drop forming orifice for forming drops of parenteral fluid ofpredetermined size and has an outlet opening which is at least as largeas its inlet opening. The drop former is formed from a plastic whichabsorbs less than about 0.03 percent by weight water. It has been foundthat the volume of the drops formed at the outlet opening of the dropformer will not vary significantly with time or parenteral fluid flowrate. Examples of plastics which absorb less than about 0.03 percent byweight water are polyethylene, polypropylene, polytetrafluoroethyleneand fluorinated ethylene propylene. Of these materials, polypropylene ismost preferred.

The plastics such as polypropylene from which the drop former of thepresent invention is formed are not well suited for forming piercersbecause of their lack of sufficient rigidity and because of theirinability to be adhesively attached to the materials such as polyvinylchloride from which drip chambers are conventionally formed.Accordingly, the drop former is typically formed of suitable size andshape so that it can be inserted into the parenteral fluid dischargeopening of a conventional piercer. The drop former of the presentinvention is preferably formed to accept a conventional metal cannula sothat it can be adapted for use where the measurement of very small flowrates is required, such as in pediatric applications.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view of a conventionalintravenous set incorporating the drop former of the present invention.

FIG. 2 is an enlarged, exploded view of the piercer and drop former ofFIG. 1. FIG. 3 is an enlarged, vertical cross-sectional view of thepiercer and drop former of FIG. 1.

DESCRIPTION or THE PREFERRED EMBODIMENTS Referring to FIG. I,intravenous set includes piercer 12 for insertion into a parenteralfluid container, flexible plastic tube 14, typically polyvinyl chloridetubing, for transporting the parenteral fluid from the container to thepatient, and needle adapter 16 to which an intravenous needle can beattached. Intravenous set 10 also includes clamp 18 for closing theinternal bore of flexible tubing 14 to control the flow rate of theparenteral fluid. the flow rate is determined by use of drip chamber 20,attached to the base of piercer l2. Drip chamber 20 is formed from atransparent material, typically flexible polyvinyl chloride. Drop former22 of the present invention is shown attached to piercer l2 and incommunication with drip chamber 20.

In using intravenous set 10, clamp 18 is closed and V piercer 12inserted into a parenteral fluid container (not shown). The container isthen appropriately suspended and the flow of parenteral fluid isstarted, such as by squeezing drip chamber 20 until it is partiallyfull. An intravenous needle (not shown) is attached to needle adapter16, and clamp 18 opened to allow the parenteral fluid to displace air intubing 14, needle adapter 16, and the intravenous needle. Subsequently,clamp 18 is closed and venipuncture performed. The flow rate ofparenteral fluid is then adjusted by using clamp 18. Parenteral fluidflows out of the parenteral fluid container through piercer 12, isformed into drops of known size in drop former 22, and falls throughdrip chamber 20, wherein the drip count can be visually observed todetermine the flow rate.

Referring now to FIG. 2, piercer 12 comprises base 24 and piercingmember 26. Piercing member 26 has sharpend 28 for piercing the closureof parenteral fluid container. Base 24 of piercer 12 includes laterallyextending projection 30 which is closed by air filter cap 32. Filter cap32 contains semipermeable air filter material which is permeable to airbut impermeable to liquid at the pressure differentials encountered, andserves to filter incoming air for venting the parenteral fluidcontainer. A typical air filter material comprises a thin mat of feltedmicroscopic fibers of Teflon on a woven fiberglass substrate. Dripchamber 20 is adhesively attached to annular flange 34 which projectsfrom the base 24 of piercer 12. Base 24 of piercer 12 also includescylindrical projection 36 to which drop former 22 is attached. Piercer12 is typically formed from a moldable plastic such asstyrene-acrylonitrile, nylon, or rigid polyvinyl chloride.

Drop former 22 includes a cylindrical base portion 38, taperedintermediate portion 40, and cylindrical top portion 42. Taperedintermediate portion 40 is of smaller diameter than cylindrical baseportion 38 forming annular shoulder 44 therebetween. The bottom of baseportion 38 is tapered inwardly at 46. Drop former 22 is formed from aplastic which absorbs less than about 0.03 percent by weight water whenmeasured over a twenty-four hour period. Examples of suitable plasticsare polyethylene having a moisture absorption of less than 0.01 percent,polypropylene having a moisture absorption of less than 0.01 to 0.03percent, and polytetrafluoroethylene and fluorinated ethylene propylene,each having a moisture absorption of about 0.01 percent. Polyethyleneand polypropylene are the generally preferred plastics, withpolypropylene being the most preferred because it is somewhat strongerthan polyethylene. Fluorinated ethylene propylene has suitable moistureabsorption properties, but is not preferred because of its cost,mechanical strength, and difficulty in moulding. By contrast, thematerials from which the piercer is formed have much higher moistureabsorption characteristics over a 24 hour period. For example,styrene-acrylonitrile absorbs about 0.2 to 0.35 percent moisture over a24 hour period. Nylon absorbs even more moisture, in the range of about0.4 to 1.8 percent. The polyvinyl chlorides are also unsuitable,absorbing from 0.2 to 1 percent by weight moisture over a 24 hourperiod.

Turning now to FIG. 3, piercer 12 defines parenteral fluid passage 48,having opening in piercing member 26 for communicating with theparenteral fluid container and discharge opening 52 in base 24 for communicating with drip chamber 20. Piercer 12 also includes vent passage 54for venting the parenteral fluid container. Vent passage 54 includeslongitudinally extending portion 56 which is substantially parallel toparenteral fluid passage 48 and has opening 58 in piercing member 26 forcommunicating with the parenteral fluid container. Vent passage 54 alsoincludss laterally extending portion 60 having opening 62 in laterallyextending projection 30. Opening 62 is closed by air filter cap 32 forfiltering incoming air. It should be understood that vent passage 54 isonly required in piercers for use with parenteral fluid containers whichdo not have a separate vent tube. One end of drop former 22 is insertedinto discharge opening 52 in piercer 12 so that tapered intermediateportion 40 forms a tight friction fit therewith and annular shoulder 44abuts the end of cylindrical portion 36. Drop former 22 forms drops ofpredetermined size, which function is normally provided by dischargeopening 52 in piercer 12.

Turning now to FIG. 4, body 64 of drop former 22 defines parenteralfluid passage 66 having opening 68 in top cylindrical portion 42 forcommunicating with parenteral fluid passage 48 in piercer l2. Parenteralfluid passage 66 also has opening 70 in cylindrical base portion 38 forcommunicating with drip chamber 20. Parenteral fluid passage 66 includescylindrical inlet and outlet portions 72 and 74, respectively.Cylindrical inlet portion 72 merges into frusto-conical intermediateportion 76, which in turn merges into tapered portion 78. The outlet endof tapered portion 78 merges into the inlet end of cylindrical outletportion 74. Parenteral fluid passage 66 tapers outwardly from inletopening 79 of frusto-conical intermediate portion 76 to near outletopening 70 so that outlet opening 70 is of larger diameter than theinlet opening 79 of frustoconical intermediate portion 76. Parenteralfluid passage portions 74, 76 and 78 together form the drop formingorifice of drop former 22. It is preferred that the ratio of the lengthto outlet diameter of the drop forming orifice be at least 2:1 or, inother words, that the combined length of portions 74, 76 and 78 ofparenteral fluid passage 66 be at least twice as long as the diameter ofoutlet opening 70.

As illustrative of one embodiment of the present invention, drop former22 was formed from polypropylene having an overall length ofapproximately one-half inch. Tapered intermediate portion 40 was taperedoutwardly at l A and inwardly tapered portion 46 was formed with anangle of 30 with respect to a line drawn perpendicular to thelongitudinal centerline of drop former 22. This taper forms sharpcircular edge 80 which facilitates the formation of the drops. In thisembodiment, inlet opening 68 had a diameter of 0.032 inches and outletopening 70 a diameter of 0.160 inches. Intermediate tapered portion 78of parenteral fluid passage 66 was tapered at an angle of 4 andfrusto-conical section 76 was tapered at an angle of approximately 26".With this arrangement, fifteen drops of parenteral fluid formed atoutlet opening 70 for each milliliter of parenteral fluid flowedtherethrough under standard intravenous set operating pressures.Further, the drop size was found to remain constant even after soakingthe drop former overnight in 5 percent dextrose and lactated Ringerssolution, respectively.

Referring now to FIGS. 5 and 6, drop former 22 is shown in use withcannula 82, typically formed from stainless steel, which is used forforming small drops suitable for measuring small flow rates such as usedin pediatric applications. In this arrangement, cylindrical inletportion 72 of parenteral fluid passage 66 forms a sleeve into whichcannula 82 is inserted. Cylindrical inlet portion 72 has a slightlysmaller inner diameter than the outer diameter of cannula 82, so thatcannula 82 can be friction fitted in drop former 22. Cannula 82 definescylindrical passage 84, having inlet opening 86 for communicating withparenteral fluid passage 48 in piercer l2 and outlet opening 88 forcommunicating with drip chamber 20. Outlet opening 88 is typically ofsuitable size for forming 60 drops of parenteral fluid for eachmilliliter flowed therethrough.

FIG. 7 shows a modified form of the drop former of the presentinvention. Drop former 90 is shown inserted in parenteral fluiddischarge opening 92 in cylindrical projection 94 of the base 96 of apiercer such as shown in FIG. 1. Drop former 90 includes cylindricalbase portion 98 and tapered top portion 100. Tapered top portion 100 isof smaller diameter than cylindrical base portion 98 forming annularshoulder 102 therebetween. Annular ring collar 104 extends around topportion 100 of drop former 90 and is adapted to contact the internalsurface of parenteral fluid discharge opening 108 when the bottom ofcylindrical portion 94 of the piercer contacts shoulder 102 of dropformer 90. A typical height for collar 104 would be approximately 0.004inches. Otherwise, drop former 90 is the same as drop former 22. Aspreviously mentioned, adhesive will not adhere to plastics such aspolypropylene which are used for forming the drop former of the presentinvention, but it will adhere to plastics such as styreneacrylonitrilewhich are used in forming a piercer. In the modified form of the dropformer shown in FIG. 7, adhesive 109 can be placed in annular opening106 defined between annular projection 94 of the piercer and tapered topportion 100 of drop former 90. The adhesive adheres to the inner surfaceof parenteral fluid passage 108 of the piercer but does not adhere tothe outer surface of tapered top portion of drop former 90. However,ring collar 104 forms a mechanical lock with adhesive 109, therebypreventing drop former 90 from being inadvertently removed fromparenteral fluid passage 108.

As mentioned previously, it has been found that the size of the dropsformed at the drop forming orifice of a conventional piercer formed frommaterials such as styrene-acrylonitrile, nylon, or rigid polyvinylchloride becomes larger with time, with up to percent difference beingnoted over a 24 hour period. Also, variations in drop size with time andwith parenteral fluid flow rate have been noted with respect to theplastic insert for pediatric use discussed above which has a taperedparenteral fluid passage which tapers inwardly from its inlet to itsoutlet forming a passage of increasingly smaller diameter. While notdesiring to be limited by any particular theory, it is believed that thechange in drop size with time in the prior art piercers results from achange in surface tension at the interface between the liquid andplastic caused by a wetting of the surface, or possibly by an expansionof the plastic due to water absorption. Further, it is believed that thedecrease in drop size at higher flow rates found in the plasticpediatric insert is caused by insufficient viscous drag to overcome theparenteral fluid inertia, which inertia increases with the flow rate.These problems of the prior art are solved by the use of the drop formerof the present invention which is formed from the plastic which absorbsless than about 0.03 percent by weight water, so that water absorptionand surface wetting are substantially avoided. Also, the viscous dragproblems are solved by providing a drop former having a straight oroutwardly tapered flow passage.

While one or more specific embodiments of the present invention havebeen illustrated, it will be understood that there are other embodimentsfalling within the scope ofthe present invention. For example, thecylindrical inlet portion of the parenteral fluid passage of the dropformer can be dispensed with when it is not desired to adapt the dropformer for pediatric use, such as by insertion of a stainless steelcannula. Also, the general exterior shape of the drop former can bevaried to adapt it for use in combination with various size and shapedischarge openings in conventional piercers.

We claim:

1. A drop former for use with a drip chamber for determining the flowrate of a parenteral fluid, comprisingz, body means defining aparenteral fluid passage therethrough, said parenteral fluid passagehaving an inlet opening for communicating with a source of parenteralfluid and an outlet opening for communicating with a drip chamber, saidparenteral fluid passage defining a drop forming orifice for formingabout 12 to 20 drops of parenteral fluid for each millimeter of fluidflowing therethrough at the pressures encountered in intravenousfeeding, said outlet opening being at least as large as said inletopening, and said body means being formed from a plastic which absorbsless than about 0.03 percent by weight water measured over about atwenty-four hour period so that the size of said drops will notmaterially change with time or flow rate.

2. The drop former of claim 1 in which said plastic is polyethylene,polypropylene, polytetrafluoroethylene, or fluorinated ethylenepropylene.

3. The drop former of claim 1 in which said plastic is polypropylene.

4. The drop former of claim 1 in which said inlet opening is formed in aportion of said body means which is of suitable size and shape forinsertion into the discharge opening of a parenteral fluid passage in apiercer.

5. The drop former of claim 1 in which said outlet opening is largerthan said inlet opening.

6. The drop former of claim 1, in which said parenteral fluid passageincludes a portion upstream of said drop forming orifice of suitablesize for receiving a cannula for forming drops of parenteral fluid whichare smaller than said predetermined size.

7. The drop former of claim 1 in which said parenteral fluid passageincludes a frusto-conical section adjacent said inlet opening, acylindrical section adjacent said outlet opening, and a taperedintermediate section merging into said frusto-conical and cylindricalsections.

8. The drop former of claim 1 in which said body means comprises acylindrical base portion forming said outlet opening and a taperedportion attached to said base portion and forming an annular shouldertherewith for facilitating attachment of said drop former to a piercer.

9. The drop former of claim 8 in which said tapered portion has a ringcollar on the external surface thereof for the adhesive attachment ofsaid drop former to said piercer.

10. The drop former of claim 8 in which said base portion includes aninwardly tapered bottom portion which merges into said outlet openingforming a sharp cylindrical edge therewith.

11. The drop former of claim 1 in which the ratio of the length of saiddrop forming orifice to the diameter of said outlet opening is at least2:1.

12. A piercer and flow meter for an intravenous set, comprising: apiercer having a base and a piercing member with a sharp end forpiercing the closure of a parenteral fluid container, said piercerdefining a parenteral fluid passage for transferring parenteral fluidfrom said container, said parenteral fluid passage having an opening insaid piercing member for communicating with said container and adischarge opening in said base; a drip chamber attached to said piercerand communicating with said discharge opening; and a drop formerattached to said piercer and comprising body means defining a parenteralfluid passage therethrough, said parenteral fluid passage having aninlet opening communicating with said discharge opening in said piercerand an outlet opening communicating with said drip chamber, saidparenteral fluid passage defining a drop forming orifice for formingdrops of parenteral fluid of predetermined size which can be visuallyobserved while falling through said drip chamber for determining theflow rate of said parenteral fluid, said outlet opening being at leastas large as said inlet opening, and said body means being formed from aplastic which absorbs less than about 0.03 percent by weight watermeasured over about a 24 hour period so that the size of said drops willnot materially change with time of flow rate.

13. The piercer and flow meter of claim 12 in which said plastic ispolyethylene, polypropylene, polytetrafluoroethylene, or fluorinatedethylene propylene.

14. The piercer and flow meter of claim 12 in which said plastic ispolypropylene.

15. The piercer and flow meter of claim 12 in which the outlet openingin said drop former is larger than said inlet opening.

16. The piercer and flow meter of claim 12 in which the parenteral fluidpassage in said drop former includes a portion upstream of said dropforming orifice of suitable size for receiving a cannula for formingdrops of parenteral fluid which are smaller than said predeterminedsize.

17. The piercer and flow meter of claim 12 in which the parenteral fluidpassage of said drop former includes a frusto-conical section adjacentsaid inlet opening, a cylindrical section adjacent said outlet opening,and a tapered intermediate sect-ion merging into said frusto-conical andcylindrical sections.

18. the piercer and flow meter of claim 12 in which the body means ofsaid drop former comprises a cylindrical base portion forming saidoutlet opening and a tapered portion attached to said base portion andforming an annular shoulder therewith for facilitating attachment ofsaid drop former to said piercer.

19. The piercer and flow meter of claim 18 in which the tapered portionof said drop former has a ring collar on the external surface thereoffor enabling the adhesive attachment of said drop former to saidpiercer.

20. The piercer and flow meter of claim 18 in which the base portion ofsaid drop former includes an inwardly tapered bottom portion whichmerges into said outlet opening forming a sharp cylindrical edgetherewith.

21. The piercer and flow meter of claim 12 in which the outlet openingof said drop former defines a drop forming orifice for forming drops ofparenteral fluid of such predetermined size that from 12 to 20 drops areformed for each milliliter of fluid flowing therethrough.

22. The piercer and flow meter of claim 12 in which the ratio of thelength of said drop forming orifice to the diameter of said outletopening is at least 2:1.

1. A drop former for use with a drip chamber for determining the flowrate of a parenteral fluid, comprising:, body means defining aparenteral fluid passage therethrough, said parenteral fluid passagehaving an inlet opening for communicating with a source of parenteralfluid and an outlet opening for communicating with a drip chamber, saidparenteral fluid passage defining a drop forming orifice for formingabout 12 to 20 drops of parenteral fluid for each millimeter of fluidflowing therethrough at the pressures encountered in intravenousfeeding, said outlet opening being at least as large as said inletopening, and said body means being formed from a plastic which absorbsless than about 0.03 percent by weight water measured over about atwenty-four hour period so that the size of said drops will notmaterially change with time or flow rate.
 2. The drop former of claim 1in which said plastic is polyethylene, polypropylene,polytetrafluoroethylene, or fluorinated ethylene propylene.
 3. The dropformer of claim 1 in which said plastic is polypropylene.
 4. The dropformer of claim 1 in which said inlet opening is formed in a portion ofsaid body means which is of suitable size and shape for insertion intothe discharge opening of a parenteral fluid passage in a piercer.
 5. Thedrop former of claim 1 in which said outlet opening is larger than saidinlet opening.
 6. The drop former of claim 1, in which said parenteralfluid passage includes a portion upstream of said drop forming orificeof suitable size for receiving a cannula for forming drops of parenteralfluid which are smaller than said predetermined size.
 7. The drop formerof claim 1 in which said parenteral fluid passage includes afrusto-conical section adjacent said inlet opening, a cylindricalsection adjacent said outlet opening, and a tapered intermediate sectionmerging into said frusto-conical and cylindrical sections.
 8. The dropformer of claim 1 in which said body means comprises a cylindrical baseportion forming said outlet opening and a tapered portion attached tosaid base portion and forming an annular shoulder therewith forfacilitating attachment of said drop former to a piercer.
 9. The dropformer of claim 8 in which said tapered portion has a ring collar on theexternal surface thereof for the adhesive attachment of said drop formerto said piercer.
 10. The drop former of claim 8 in which said baseportion includes an inwardly tapered bottom portion which merges intosaid outlet opening forming a sharp cylindrical edge therewith.
 11. Thedrop former of claim 1 in which the ratio of the length of said dropforming orifice to the diameter oF said outlet opening is at least 2:1.12. A piercer and flow meter for an intravenous set, comprising: apiercer having a base and a piercing member with a sharp end forpiercing the closure of a parenteral fluid container, said piercerdefining a parenteral fluid passage for transferring parenteral fluidfrom said container, said parenteral fluid passage having an opening insaid piercing member for communicating with said container and adischarge opening in said base; a drip chamber attached to said piercerand communicating with said discharge opening; and a drop formerattached to said piercer and comprising body means defining a parenteralfluid passage therethrough, said parenteral fluid passage having aninlet opening communicating with said discharge opening in said piercerand an outlet opening communicating with said drip chamber, saidparenteral fluid passage defining a drop forming orifice for formingdrops of parenteral fluid of predetermined size which can be visuallyobserved while falling through said drip chamber for determining theflow rate of said parenteral fluid, said outlet opening being at leastas large as said inlet opening, and said body means being formed from aplastic which absorbs less than about 0.03 percent by weight watermeasured over about a 24 hour period so that the size of said drops willnot materially change with time of flow rate.
 13. The piercer and flowmeter of claim 12 in which said plastic is polyethylene, polypropylene,polytetrafluoroethylene, or fluorinated ethylene propylene.
 14. Thepiercer and flow meter of claim 12 in which said plastic ispolypropylene.
 15. The piercer and flow meter of claim 12 in which theoutlet opening in said drop former is larger than said inlet opening.16. The piercer and flow meter of claim 12 in which the parenteral fluidpassage in said drop former includes a portion upstream of said dropforming orifice of suitable size for receiving a cannula for formingdrops of parenteral fluid which are smaller than said predeterminedsize.
 17. The piercer and flow meter of claim 12 in which the parenteralfluid passage of said drop former includes a frusto-conical sectionadjacent said inlet opening, a cylindrical section adjacent said outletopening, and a tapered intermediate section merging into saidfrusto-conical and cylindrical sections.
 18. the piercer and flow meterof claim 12 in which the body means of said drop former comprises acylindrical base portion forming said outlet opening and a taperedportion attached to said base portion and forming an annular shouldertherewith for facilitating attachment of said drop former to saidpiercer.
 19. The piercer and flow meter of claim 18 in which the taperedportion of said drop former has a ring collar on the external surfacethereof for enabling the adhesive attachment of said drop former to saidpiercer.
 20. The piercer and flow meter of claim 18 in which the baseportion of said drop former includes an inwardly tapered bottom portionwhich merges into said outlet opening forming a sharp cylindrical edgetherewith.
 21. The piercer and flow meter of claim 12 in which theoutlet opening of said drop former defines a drop forming orifice forforming drops of parenteral fluid of such predetermined size that from12 to 20 drops are formed for each milliliter of fluid flowingtherethrough.
 22. The piercer and flow meter of claim 12 in which theratio of the length of said drop forming orifice to the diameter of saidoutlet opening is at least 2:1.